Isolated mammalian chromosomes have been quantitatively classified by high resolution flow cytometry. Chinese hamster chromosomes stained with 33258 Hoechst and excited in the UV showed a fluorescence distribution in which the 14 types of Chinese hamster chromosomes were resolved into 16 groups seen as distinct peaks in the distributions. Chinese hamster chromosomes were also stained with both 33258 Hoechst (HO) and chromomycin A3 (CA3); the two dye contents were measured by selective excitation in the UV and at 458 nm in a dual beam flow cytometer. The resulting two parameter distribution (HO versus CA3) showed 10 chromosome groups1. Human strain LLL 761 chromosomes stained with HO and excited in the UV showed a fluorescence distribution in which the 23 types of human chromosomes were resolved into 12 groups. Human chromosomes stained with both HO and CA3 and measured in the dual beam flow cytometer produced two parameter fluorescence distributions which showed 20 groups. The chromosomes associated with each group were determined by quinacrine banding analysis of sorted chromosomes and by DNA cytophotometry of preidentified metaphase chromosomes. The relative HO and CA3 stain content and frequency of occurrence of chromosomes in each group were determined from the fluorescence distributions and compared to the results from DNA cytophotometry. The chromosome to chromosome variations in HO and CA3 staining are attributed to variations in chromosomal base composition.
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